91209 has 4 divisors (see below), whose sum is σ = 121616. Its totient is φ = 60804.

The previous prime is 91199. The next prime is 91229. The reversal of 91209 is 90219.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 91209 - 2⁴ = 91193 is a prime.

It is a D-number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (91229) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15199 + ... + 15204.

It is an arithmetic number, because the mean of its divisors is an integer number (30404).

2⁹¹²⁰⁹ is an apocalyptic number.

It is an amenable number.

91209 is a deficient number, since it is larger than the sum of its proper divisors (30407).

91209 is a wasteful number, since it uses less digits than its factorization.

91209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30406.

The product of its (nonzero) digits is 162, while the sum is 21.

The square root of 91209 is about 302.0082780322. The cubic root of 91209 is about 45.0138229140.

Subtracting from 91209 its reverse (90219), we obtain a triangular number (990 = T₄₄).

It can be divided in two parts, 91 and 209, that added together give a triangular number (300 = T₂₄).

The spelling of 91209 in words is "ninety-one thousand, two hundred nine".